The tree · Drive · Happens to the world · Could be decided within 5 to 20 years
A nuclear-powered engine produces a kilometre per second of velocity change in space
Nuclear propulsion, whether a reactor heating propellant directly or a reactor driving electric thrusters, has been designed and ground-tested for sixty years, and no nuclear-powered system has ever produced a meaningful orbit change: SNAP-10A's reactor ran an ion thruster briefly in orbit in 1965, without moving the vehicle to speak of. The first in-space burn that substantially moves a vehicle is the step from paper to hardware, and it is what routine nuclear propulsion, one route to the fast transit Tier 3 requires, has to start from.
The test: what counts as it having happened
A spacecraft in space accumulates a velocity change of at least one kilometre per second from its propulsion itself, excluding gravitational effects, using propulsion powered by a nuclear reactor, confirmed by the operator and by independent orbital tracking.
Settled by: The operator's mission record and independent orbital tracking
The odds, by how long I live
| baselineto 2071 ± 8 | moderateto 2080 | strongto 2095 | radicalto 2136 | openno deadline |
|---|---|---|---|---|
| 60% | 72% | 85% | 93% | 95% |
Each column is a different guess at how long I live, from current trends (baseline) to open-ended. The number is the chance this happens before that deadline, assuming everything it depends on happens first. As of September 19th, 2026.
Why these numbers: Sixty years of ground tests and no meaningful flight, and the most recent flight demonstration program was cancelled in 2025; it needs a mission only nuclear can do.
What this one is worth
If this happened tomorrow and nothing else changed, the chance that I live and work off Earth by 2071 goes from 0.5% to 0.4% (−0.1 points). If it turned out no, the same number goes to 0.5% (too small to tell apart from chance).
| Longevity scenario | baseline2071 ± 8 | moderate2080 | strong2095 | radical2136 | openno deadline |
|---|---|---|---|---|---|
| The headline as it stands | 0.5% | 1.2% | 3.8% | 11% | 15% |
| If this settled yes now | 0.4% | 1.4% | 3.8% | 11% | 15% |
| If this settled no now | 0.5% | 1.2% | 3.6% | 10% | 15% |
This is what the site says in advance, before the thing happens. When it does, the
ledger entry that records it quotes this figure beside what actually followed, so a
reader can see whether the prediction held. Worked out at the run
2026-10-11-scan by holding this step at each outcome in turn and
playing the whole tree out again, 20,000 times per
scenario. That is a throw of the dice, so a move smaller than about
0.10 points is inside the noise rather than
a finding.
What the ledger says about this step
- Forty-one steps had their criteria tightened so that two readers would agree when each has happened, with no number moved for that alone 2026-09-20 The tree itself changed
The last 3 checks
Once a week the tree is read against the news, node by node, against the test above. Open a line to see what that week held. Every check ever made on this node is on the Radar page.
-
2026-11-01 No change
On October 8th, 2026 NASA and the Department of Energy signed an agreement on nuclear electric propulsion, and on October 20th, 2026 trade press reported progress on the SR-1 Freedom power module, with launch still targeted for December 2028. These are plans and hardware progress, not accumulated velocity change in space, and the DRACO thermal demo has no reported flight.
-
2026-10-04 Nothing new
No reactor-powered spacecraft has flown or accumulated delta-v in the window; DARPA DRACO was cancelled in 2025 and SR-1 Freedom remains a plan for a December 2028 launch.
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2026-09-19 No change
DRACO remains cancelled after its FY2026 budget was zeroed in 2025, with no formal successor. NASA ran a ground cold-flow test campaign from July to September 2026 on a nuclear-electric propulsion engineering unit, and the Space Reactor-1 Freedom demonstrator still targets a 2028 launch. No in-space orbit change has occurred.
Revisions
| Date | Field | From | To | Why |
|---|---|---|---|---|
| 2026-09-19 | name | A nuclear-powered engine changes a spacecraft's orbit in space for the first time | A nuclear-powered engine produces a kilometre per second of velocity change in space | Step 27 outside-model review, item 72 (docs/reviews/2026-09-19-rulings.md): the name says 'first time' and the description said 'never flown', but SNAP-10A powered an ion thruster in orbit in 1965 (NASA's own assessment, fetched); the name now says what the criterion measures. Decided September 19th, 2026. |
| 2026-09-19 | resolution | 'changes its velocity by at least one kilometre per second' | cumulative velocity change of at least one kilometre per second from the propulsion itself, excluding gravitational effects | Step 27 outside-model review, item 72: the bar is the same, stated so that a gravity assist cannot be counted. Decided September 19th, 2026. |
| 2026-09-19 | description | 'never flown' | no nuclear-powered system has produced a meaningful orbit change; SNAP-10A ran an ion thruster briefly in 1965 | Step 27 outside-model review, item 72: factual correction, verified against NASA's space-nuclear-systems assessment on September 19th, 2026. Decided September 19th, 2026. |
| 2026-09-25 | description | 'routine nuclear propulsion, the Tier 3 criterion' | 'routine nuclear propulsion, one route to the fast transit Tier 3 requires' | Candidate 6 of docs/proposal-function-over-route-2026-09-25.md, I approved September 25th, 2026: Tier 3 now requires D-fast-transit-in-routine-use, with routine nuclear propulsion as one route. Text only. |
Notes
Shares a technology base with the lunar surface reactor (an energy node); whether that is a hard dependency is for step 7. SNAP-10A (1965): reactor-powered ion thruster ran briefly during a 43-day mission and produced no meaningful orbit change; the node stays open.
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The record itself is data/D-drive.toml in the public repository.